A Cluster Analysis Approach To Classifying Irish Native Woodlands

Abstract

The National Survey of Native Woodlands in Ireland, which was initiated in 2003, will provide two key resources identified in the National Biodiversity Plan: an inventory of native woodlands and a woodland classification system. The project has taken advantage of recent advances in GIS and remote sensing to develop a GIS-based inventory of potentially native woodland sites. Field survey and characterisation of a large subset of these sites is currently ongoing. In this paper, a proposed methodology is presented for developing a national woodland classification based on data from this field survey using current best practice in statistical techniques. The applicability of this method is demonstrated using the data gathered thus far. The method uses hierarchical agglomerative cluster analysis and indicator species analysis with validation using multi-response permutation procedure (MRPP) and non-metric multidimensional scaling ordination (NMS). A two-tier classification system has been produced, with five broad groups of woodland being each divided into a number (between five and eight) of more specific woodland types. The five main vegetation groups were named, using the results of indicator species analysis, as: Quercus petraea Luzula sylvatica , Quercus robur Hedera helix , Corylus avellana Thamnobryum alopecurum, Alnus glutinosa Filipendula ulmaria and Betula pubescens Molinia caerulea . This classification defines a greater number of woodland types than previous studies based on the more subjective central European phytosociological approach. However, for applied purposes any evaluation based on the statistical significance of these groups may need to be tempered by ecological significance. It is apparent that the identification of native woodland communities may be hampered by the modified nature of Irish woodlands and the presence of non-native species in particular. With the dataset still expanding, the results must be regarded as preliminary, but it is concluded that this is an effective method for the objective classification of Irish native woodlands.